1. Field of the Invention
The present invention relates to a method for manufacturing a printed circuit board.
2. Background of the Related Art
FIG. 1 is a diagram that shows a plan view of a related art printed circuit board. As shown in FIG. 1, a printed circuit board 1 is cut along a dotted line to form one product portion 1′. The product portion 1′ is used as a product.
A chip mounting area 2 is formed on the center of the product portion 1′. A semiconductor chip (not shown) is mounted on the chip mounting area 2 of the product portion 1′. A plurality of wire bonding pads 3 are formed along the perimeter of the chip mounting area 2. The wire bonding pads 3 are connected to the semiconductor chip by gold wires (not shown), thereby electrically connecting the semiconductor chip to the printed circuit board 1. The wire bonding pads 3 are exposed from the surface of the printed circuit board 1. The exposed surfaces of the wire bonding pads 3 are plated with gold (Au). The wire bonding pads 3 are electrically connected to circuit patterns (not shown) formed on the printed circuit board 1.
A plurality of ball pads 4 are formed on the printed circuit board 1. Solder balls (not shown) are attached to the ball pads 4 of the printed circuit board 1, thereby electrically connecting the printed circuit board 1 to an external substrate. The surfaces of the ball pads 4 are also plated with gold (Au), to improve adhesive strength of bonding between the ball pads 4 and the solder balls. The ball pads 4 are also electrically connected to the circuit pattern (not shown) formed on the printed circuit board 1. Therefore, the ball pads 4 are electrically connected to the wire bonding pads 3.
In order to plate the wire bonding pads 3 and the ball pads 4 with gold (Au), electric power should be supplied to the wire bonding pads 3 and the ball pads 4. Therefore, a main power supply line 6 for supplying power is disposed along the perimeter of the product portion 1′ of the printed circuit board 1. The main power supply line 6 is shaped in a circuit pattern and has a predetermined width.
Sub power supply lines 5 are connected between the main power supply line 6 and the wire bonding pads 3 and the ball pads 4, respectively. The sub power supply lines 5 have a smaller width than that of the main power supply line 6. The sub power supply lines 5 serve to supply power to each of the wire bonding pads 3 and the ball pads 4. FIG. 1 shows a portion of the sub power supply lines 5, which are connected to the wire bonding pads 3 and the ball pads 4. Actually, the sub power supply lines 5 are connected to all (not shown) of the wire bonding pads 3 and the ball pads 4 one by one. The sub power supply lines 5 are electrically connected to the main power supply line 6 formed along the perimeter of the product portion 1′.
Therefore, when power is supplied to the main power supply line 6 to plate the wire bonding pads 3 and the ball pads 4 with gold (Au), the power is transmitted to the wire bonding pads 3 and the ball pads 4 via the sub power supply lines 5 connected to the main power supply line 6. Accordingly, the surfaces of the wire bonding pads 3 and the ball pads 4 are plated with gold (Au).
The main power supply line 6 and the sub power supply lines 5 are formed in a manufacturing process of the printed circuit board 1, and are shaped in circuit patterns. A guide hole 7 is for setting a position of the printed circuit board 1.
However, as described above the related art printed circuit board has various problems. As the semiconductor chip is highly integrated, many wire bonding pads 3 for electrically connecting the semiconductor chip to the printed circuit board 1 are required, and many ball pads 4 for electrically connecting the printed circuit board 1 to the external substrate are required. Further, as the semiconductor product is miniaturized, a small-sized printed circuit board is required. To reduce the size of the printed circuit board, the wire bonding pads 3 and the ball pads 4 should be finely disposed, and the sub power supply lines 5 connected to the wire bonding pads 3 and the ball pads 4 should be finely and exactly designed.
The sub power supply lines 5 pass between the wire bonding pads 3 and the ball pads 4, and then are connected to the corresponding one of the wire bonding pads 3 and the ball pads 4. After the gold (Au)-plating process or further process, the printed circuit board 1 is cut along the dotted line, thereby forming the product portion 1′. The product portion 1′ is used as a product.
However, after cutting the printed circuit board 1, portions of the sub power supply lines 5 are left on the product portion 1′. As the semiconductor chip is highly integrated and is operated at high-frequencies, signals from the semiconductor chip flow along the portions of the sub power supply lines 5 that remain on the product portion 1′ to cause the interference with neighboring remaining sub power supply lines 5 and decrease the performance of the semiconductor product.
To solve such a problem, an edge back technique for removing the left behind sub power supply lines 5 has been introduced. In the edge back technique, the sub power supply lines 5 are coated with a gold-plating resist. The wire bonding pads 3 and the ball pads 4 are plated with gold (Au). Then, the gold-plating resist is removed from the sub power supply lines 5, thereby exposing the sub incoming lines 5. Next, the exposed sub power supply lines 5 are removed using an alkali etching solution.
However, in order to prevent the wire bonding pads 3 and the ball pads 4 from being removed by the etching solution together with the sub power supply lines 5, connection parts of the sub power supply lines 5 with the wire bonding pads 3 and the ball pads 4 having a prescribed length are still left behind. Further, since a photoresist is used as the gold-plating resist, it is difficult to coat the photoresist exactly on the sub power supply lines 5 because of a positional deviation of the resist. Further, it is difficult to adhere the photoresist closely to the sub incoming lines 5 because of a weak adhesive strength of the resist. Therefore, the sub power supply lines 5 are not entirely removed. Alternatively, a full body plating method has been introduced. However, since the full body plating method damages the circuit patterns formed on the printed circuit board 1, it is difficult to form fine circuit patterns. Thus, there exists a need to provide electric power for plating ball pads and bonding pads of a printed circuit board.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.